Imidazoline compound, mobility control system, plugging agent for gas channeling, and method for carbon dioxide flooding

ABSTRACT

An imidazoline compound, a mobility control system, a plugging agent for gas channeling, and a method for carbon dioxide flooding. The structure of the imidazoline compound is represented by formula (1), in which R is pentadecyl, heptadecenyl, or heptadecyl. A mobility control system that contains the imidazoline compound can interact with carbon dioxide to form a plugging agent for gas channeling, and thereby attains a plugging effect for carbon dioxide channeling in a carbon dioxide flooding process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/716,207, filed on Sep. 26, 2017, entitled “Imidazoline Compound,Mobility Control System, Plugging Agent For Gas Channeling, And MethodFor Carbon Dioxide Flooding”, and claims priority to Chinese ApplicationNo. 201710566128.8, filed on Jul. 12, 2017, entitled “Mobility ControlSystem for Carbon Dioxide Flooding in Low permeability or Ultra-lowPermeability Oil Reservoirs and Use Thereof”, which are specifically andentirely incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the field of oil recovery efficiencyimprovement, in particular to an imidazoline compound, a mobilitycontrol system that contains the imidazoline compound, a plugging agentfor gas channeling formed by the mobility control system, and a methodfor carbon dioxide flooding utilizing the mobility control system.

BACKGROUND OF THE INVENTION

As a highly efficient energy resource, petroleum plays an irreplaceablerole in the national economy. As the national economy in China growsrapidly, the demand for petroleum is increasing continuously. In year2015, the domestic yield of crude oil was 213 million tons, and thequantity of imported crude oil was 334 million tons, and theforeign-trade dependency was as high as 62%. Hence, efficientexploitation of petroleum is a major demand and important safeguard fornational energy security.

As oil and gas exploration and development is deepened, the percentageof exploration and development of low-permeability oil and gas resourceshas become higher and higher. The average exploration and developmentpercentage of low-permeability oil and gas resources has accounted forabout 67% of newly increased proven reserves during the 12^(th) 5-yearplan; especially in recent years, new proven ultra-low permeability oilreservoirs were especially abundant. In China, ultra-low permeabilityoil and gas resources have been regarded as a major domain of nationaloil and gas development.

The oil recovery of ultra-low permeability oil reservoirs recovered bymeans of natural energy is usually lower than 10%. To improve the oilrecovery of those oil reservoirs, the oil reservoir energy has to besupplemented by water or gas injection. However, in a water injectionprocess, a hydrated film may be formed easily, and the clay minerals inthe formation swell and the pores tend to be closed when the clayminerals encounter water, resulting in rapidly increased injectionpressure and severely decreased injection volume or even failure ofinjection; consequently, the recovery efficiency of the matrix is verylow. Compared with water injection, injected gas is easier to permeateinto micro-nano pores, and can effectively displace the crude oil in thematrix; therefore, the oil displacement efficiency can be remarkablyimproved. Especially, carbon dioxide is usually more dissoluble in waterthan hydrocarbon gasses, and has higher dissolvability in crude oil thanin water. Carbon dioxide dissolved in a water solution can transfer todissolve in crude oil, and has advantages including high mobility,viscosity reduction, volumetric expansion, interfacial tensionreduction, plugging removal by acidization, light hydrocarbonextraction, and easy phase-mixing features, etc. Therefore, carbondioxide flooding has received extensive concern as an effective methodfor enhancing oil recovery for low-permeability oil reservoirs in Chinaand foreign countries, and has achieved favorable effects inapplications in oil fields. However, oil reservoirs with ultra-lowpermeability are usually accompanied with natural and/or artificialfractures. As a result, after carbon dioxide is injected into theformation, since the viscosity of carbon dioxide is much lower than thatof water, gas channeling may occur easily along the fractures;therefore, the swept volume of carbon dioxide and the oil displacementefficiency are severely decreased, so that the field experiment resultis severely degraded. In recent years, domestic and foreign researchershave put forward 5 types of mobility control systems that can be used inthe carbon dioxide flooding process and associated methods:

Water Alternating Gas (WAG)

The Water Alternating Gas (WAG) method is the most widely applied andmost successful carbon dioxide mobility control method. WAG is to injectwater slugs and gas slugs alternatively to the oil reservoir, wherein,water firstly enters into the fractures and form a shield; since a phaseinterface exists between water and gas, the water saturation isincreased, while the gas saturation is decreased, and thereby therelative permeability of carbon dioxide is decreased, the gas transfersinto the matrix, the gas-to-oil mobility ratio is improved, the sweptvolume of gas is expanded, and the purpose of improving oil recovery isattained. However, for oil reservoirs with ultra-low permeability, thefollow-up injection is very difficult, and the introduced water willhamper carbon dioxide from mixing with hydrocarbon compounds.

Foam

A foamed system has a “selective plugging” characteristic. The foams caneffectively decrease the relative permeability of gas in the porousmedia, and thereby can effectively control gas mobility in the carbondioxide injection process; in addition, foam flooding applied in oilfields is relatively successful. The foam flooding effect generated byinjecting a surfactant and a gas simultaneously is more advantageousthan that generated by injecting the surfactant and the gasalternatively; in addition, by comparing the effect of foam flooding inimprovement of vertical sweep efficiency with the effect of polymerflooding, it is concluded that the effect of foam flooding forhigh-permeability zones is superior to that of polymer flooding. Toimprove stability of foams, polymer enhanced foam, gelled foam, andthree-phase foam are developed. However, foaming agents employed byconventional foam flooding are usually water-dissoluble surfactants.When such a surfactant is used for ultra-low permeability oilreservoirs, the solution of water-dissoluble foaming agent is difficultto inject, and consequently it is difficult to use the foam fluid tocontrol carbon dioxide mobility.

Polymer Viscosifiers

Polymers can be directly dissolved as chemical additives insupercritical carbon dioxide to attain an effect of increasing theviscosity of the supercritical carbon dioxide. Domestic and foreignresearchers have studied the influences of supercritical carbon dioxidefluid admixed with polymer viscosifiers on mobility control and sweepefficiency through laboratory experiments and field experiments. Helleret al. has found that polymers can be much more dissolved as mobilitycontrol agents in supercritical carbon dioxide, and the structure ofpolymer, chemical properties of crystal, and molecular weight, etc. havesignificant influence on the solubility of polymers in carbon dioxide.At present, polymers that have been studied extensively includefluoropolymers and ordinary polymers. Wherein, ordinary polymers arehydrophobic and usually have a problem of poor solubility, which resultsin a poor viscosifying effect; fluoropolymers have much betterdissolvability in supercritical carbon dioxide, and can attain a fairlygood viscosifying effect; however, such polymers have their obviousshortcomings: firstly, the production cost is too high to massproduction; secondly, the environmental hazard is severe, and adverse toenvironmental protection.

Gel

The channel plugging mechanism of gel is to utilize a gel solutions toform gel for plugging in the fractured matrix or channels. Withreference to gel materials for conformance control, a gel system (e.g.,sodium silicate gel) that matches the oil reservoir can be developedaccording to the actual oil reservoir conditions; specifically, waterglass gel generated through a reaction between sodium silicate solutionand carbon dioxide is utilized to inhibit carbon dioxide channeling andattain the purpose of achieving mobility control in carbon dioxideflooding. The viscosity of the system is low and equivalent to theviscosity of water; hence, the system has a characteristic of highplugging strength; however, a certain degree of contamination to thematrix of the ultra-low permeability oil reservoir will be resulted.

Precipitation

The basic plugging principle of the precipitation method is to control asalt solution (e.g., magnesium salt, calcium salt, or barium salt)hydrolyzed to an alkaline state or an organic amine (ethylene diamine)to react with injected carbon dioxide to generate carbonateprecipitation, and thereby attain an plugging effect. The chemicalprecipitation method can effectively improve the mobility of carbondioxide, and can improve the sweep efficiency by about 20-30%. However,it is necessary to note that the pH value of the solution in the actualoil reservoir or the reaction of NaOH with rocks in the oil reservoirwill make it difficult to control the pH reasonably during theconstruction process. Ethylene diamine belongs to small molecularorganic amine, and is inflammable, toxic, and harmful to health andenvironment in itself; in addition, if the oil saturation is high, theplugging strength of the generated precipitate will be decreased.

Though the above-mentioned methods have certain carbon dioxide mobilitycontrol capability, they have drawbacks such as unsatisfactory effect,complex operation, environmental pollution, and formation damage, etc.

SUMMARY OF THE INVENTION

To overcome the above-mentioned drawbacks of mobility control systemsfor carbon dioxide flooding in the prior art, the present inventionprovides an imidazoline compound, a mobility control system, a pluggingagent for gas channeling, and a method for carbon dioxide flooding.

To attain the object described above, in a first embodiment, the presentinvention provides an imidazoline compound, of which the structure isrepresented by formula (1):

wherein, R is pentadecyl, heptadecenyl or heptadecyl.

In a second embodiment, the present invention provides a mobilitycontrol system, which comprises the imidazoline compound in the presentinvention, a mobility control additive, and water.

In a third embodiment, the present invention provides a plugging agentfor gas channeling, which is a mixture obtained by introducing carbondioxide into the mobility control system in the present invention forgel forming.

In a fourth embodiment, the present invention provides a method forcarbon dioxide flooding, which comprises: injecting the mobility controlsystem in the present invention into an oil reservoir, and theninjecting carbon dioxide into the oil reservoir for over-displacement;after the mobility control system forms a plugging agent for gaschanneling, further injecting carbon dioxide into the oil reservoir foroil displacement.

The present invention has the following beneficial effects:

-   -   (1) The mobility control system in the present invention is an        intelligent carbon dioxide-sensitive material, which forms a        plugging agent for gas channeling and attains a plugging effect        for gas channeling after it contacts with carbon dioxide under        formation temperature.    -   (2) The mobility control system in the present invention is        applicable to deep plugging for gas channeling in carbon dioxide        flooding oil reservoir under 40-90° C. and can increase the        swept volume of carbon dioxide flooding; the plugging agent for        gas channeling formed by the mobility control system and carbon        dioxide has viscosity as high as 1×10⁴-20×10⁴ mPa·s.    -   (3) The components of the mobility control system in the present        invention are all environment-friendly, don't contain any toxic        chemical component, and are favorable for environmental        protection and operator's health.    -   (4) The mobility control system in the present invention has low        initial viscosity (only as low as 5-10 mPa·s). It has good        injection performance, and can deeply enter into gas channel        easily, and thereby achieves deep plugging for gas channeling.        It reduces harms to non-target zones. The mobility control        system is not only convenient to use in field operation, but        also can greatly enhance the oil recovery of the subsequent        carbon dioxide flooding.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an infrared spectrogram of 1-ethoxyl-2-pentadecyl-imidazolinein preparation example 1;

FIG. 2 is a ¹H-NMR spectrogram of 1-ethoxyl-2-pentadecyl-imidazoline inthe preparation example 1;

FIG. 3 is a viscosity comparison diagram before/after the mobilitycontrol system in example 2 interacts with carbon dioxide at 40° C.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The endpoints and any value in the ranges disclosed in the presentinvention are not limited to the exact ranges or values; instead, thoseranges or values shall be comprehended as encompassing values that areclose to those ranges or values. For numeric ranges, the endpoints ofthe ranges, the endpoints of the ranges and the discrete point values,and the discrete point values may be combined to obtain one or more newnumeric ranges, which shall be deemed as having been disclosedspecifically in this document.

In the first aspect, the present invention provides an imidazolinecompound, of which the structure is represented by formula (1):

wherein, R is pentadecyl, heptadecenyl or heptadecyl.

In the present invention, the imidazoline compound may be prepared withthe following method:

-   -   (1) R1-COOH and N-(2-ethoxyl) ethylene diamine are dissolved in        an organic solvent, the mixture is heated up to 155-160° C. and        hold at that temperature for 4 h or longer time for reflux        reaction; after the reaction is completed, unreacted        N-(2-ethoxyl) ethylene diamine and organic solvent are separated        by rotary evaporation, and thereby a crude product is obtained;        wherein, R1 is pentadecyl, heptadecenyl or heptadecyl.    -   (2) The crude product obtained in the step (1) is heated up to        230-240° C., and is held at the temperature for 4-6 h for        further reaction under a reflux condensation condition; thus, a        yellow oily liquid is obtained;    -   (3) The material obtained in the step (2) is treated by reduced        pressure distillation in hot state, the product is poured into a        mixed solution of ethyl acetate, absolute ethyl alcohol, and        petroleum ether mixed in advanced at a volume ratio of 3:3:1        before the product solidifies, the system is agitated vigorously        and then kept still so that a solid precipitates; after the        system is cooled and crystallized, it is filtered by vacuum        filtering, and flushed with the above-mentioned mixed solution;        thus, a white semi-solid material is obtained;    -   (4) The white semi-solid material obtained in the step (3) is        dissolved in ether, and then the product is treated by vacuum        filtering, washing, and drying; thus, the imidazoline compound        described in the present invention is obtained.

In the present invention, the solvent used in the preparation method maybe any solvent that can dissolve the above-mentioned raw materials inthe art; for example, the solvent may be dimethyl benzene.

In the present invention, the amount of the solvent may be selectedconventionally in the art, as long as the raw materials of the reactioncan be dissolved in the solvent; preferably, the weight ratio of theorganic solvent and N-(2-ethoxyl) ethylene diamine is 8-12:1.

In the preparation method, the amount of R₁—COOH and N-(2-ethoxyl)ethylene diamine may be selected according to the ratio of acid andamine in the target product imidazoline compound; preferably, the molarratio of R₁—COOH and N-(2-ethoxyl) ethylene diamine is 0.8-1:1.

In the second aspect, the present invention provides a mobility controlsystem, which comprises the imidazoline compound in the presentinvention, a mobility control additive, and water.

In the present invention, as an important constituent of the mobilitycontrol system, the mobility control additive has an effect of enhancingsystem mobility control. Preferably, the mobility control additive isselected from the group consisting of sodium salicylate, maleic acid,sodium p-toluene sulfonate, and combinations thereof.

According to a preferred embodiment of the present invention, R ispentadecyl, and the mobility control additive is sodiump-toluenesulfonate. In that preferred embodiment, the mobility controlsystem has a more outstanding mobility control effect.

In the present invention, there is no particular restriction on thecontents of the imidazoline compound and the mobility control additive,which is to say, the contents can be selected conventionally in the art;however, to attain a better mobility control effect, preferably, in themobility control system, the content of the imidazoline compound is 1-10wt % (e.g., 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt%, 9 wt %, or 10 wt %), the content of the mobility control additive is0.1-2 wt % (e.g., 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1 wt %, 1.1 wt %, 1.2 wt %, 1.3 wt%, 1.4 wt %, 1.5 wt %, 1.6 wt %, 1.7 wt %, 1.8 wt %, 1.9 wt %, or 2 wt%), and the content of water is 88-98.9 wt %; further preferably, in themobility control system, the content of the imidazoline compound is 2-6wt %, the content of the mobility control additive is 0.4-0.8 wt %, andthe content of water is 93.2-97.6 wt %.

The mobility control system in the present invention is an intelligentcarbon dioxide-sensitive material, which forms a gel material after itcontacts with carbon dioxide, and that gel material can attain aplugging effect for gas channeling.

In the third aspect, the present invention provides plugging agent forgas channeling, which is a mixture obtained by introducing carbondioxide into the mobility control system in the present invention forgel forming.

The viscosity of plugging agent for gas channeling in the presentinvention can reach as high as 1×10⁴-20×10⁴ mPa·s, which can fully meetthe requirements for plugging for gas channeling.

In the present invention, the volume ratio of the introduced volume ofcarbon dioxide and the volume of the mobility control system is 1-1.5:1.However, to improve the performance of the mobility control system,preferably, the introducing rate of carbon dioxide is 0.5-1.0 mL/min.

In the third aspect, the present invention provides a method for carbondioxide flooding, which comprises: injecting the mobility control systemin the present invention into an oil reservoir, and then injectingcarbon dioxide into the oil reservoir for over-displacement; after themobility control system forms a plugging agent for gas channeling,further injecting carbon dioxide into the oil reservoir for oildisplacement.

In the present invention, the method can achieve carbon dioxide floodingfor oil reservoirs within a wide temperature range; preferably, thetemperature of the oil reservoir is 40-90° C.

The method for carbon dioxide flooding provided in the present inventioncan effectively prevent carbon dioxide channeling in the carbon dioxideflooding process for low permeability or ultra-low permeability oilreservoirs; especially, for ultra-low permeability oil reservoirs, themethod for carbon dioxide flooding can increase the swept volume ofcarbon dioxide and improve the oil displacement efficiency, and therebyimprove the oil recovery efficiency of ultra-low permeability oilreservoirs.

In the present invention, for ultra-low permeability oil reservoir coresthat contain fractures in different widths (wherein, the gas loggedpermeability of the rock core matrix is about 0.3 mD, the width offractures is 1-1,000 μm), if the method provided in the presentinvention is used for carbon dioxide flooding, the plugging efficiencyof the plugging agent for gas channeling formed by the mobility controlsystem will be ≥90%.

The plugging efficiency testing method for the mobility control systemprovided in the present invention when the mobility control system isused for carbon dioxide flooding may be any conventional method in theart; for example, the plugging efficiency testing method may be:

-   -   (1) Preparing a rock core that contains fractures: the rock core        is assembled from rock core matrix blocks cut along the axial        direction manually, with gaps reserved between adjacent rock        core matrix blocks, and the width of fractures is controlled by        adding stainless steel plates and confining pressure with a core        holder;    -   (2) Oil saturation: crude oil saturation is carried out for the        rock core with fractures with vacuum pumping and pressurization        devices, and the mass of the rock core with fractures is        measured before and after crude oil saturation, so as to obtain        the mass of saturated crude oil in the rock core;    -   (3) Water flooding: water flooding is carried out at 1 mL/min        displacement rate with a rock core flooding device, till the        water cut reaches 98%;    -   (4) Carbon dioxide flooding: Carbon dioxide is injected at 1        mL/min injection rate continuously, and the gas injection        pressure is monitored; after the pressure is stabilized, the gas        injection pressure is logged, and gas logged permeability k1 is        calculated;    -   (5) Injecting mobility control system: the mobility control        system in the present invention is injected at 1 mL/min        injection rate, and then carbon dioxide is injected for        over-displacement;    -   (6) Gel forming: the rock core is sealed and held at a constant        temperature (test temperature) for 10 min., so that a plugging        material is formed extensively;    -   (7) Secondary carbon dioxide flooding: Carbon dioxide is        injected at 1 mL/min injection rate continuously again, and the        gas injection pressure is monitored; after the pressure is        stabilized, the gas injection pressure is logged, and gas logged        permeability k2 is calculated;

The permeability is calculated with the following formula:

$k = {\frac{2Q_{2}L\;\mu\; p_{0}}{A\left( {p_{1}^{2} - p_{2}^{2}} \right)} \times 10^{- 1}}$

Where, k is permeability, μm²; Q₂ is gas flow at the exit side of therock core, ml/s; L is length of rock core, cm; A is cross-sectional areaof rock core, cm²; P₀ is absolute atmospheric pressure, MPa; P₁ isabsolute pressure at the entry side of the rock core, MPa; P₂ isabsolute pressure at the exit side of the rock core, MPa; and μ is gasviscosity at the test temperature and atmospheric pressure, mPa·s.

The plugging efficiency is calculated with the following formula:plugging efficiency=(k1−k2)/k1.

In the above testing method, the rock core matrix can be commerciallyavailable; for example, E-series rock cores (permeability=0.3 mD) fromBeijing Shengwei Technology Co. Ltd. may be used; the crude oil isdehydrated and degassed crude oil from a block in Changqing Oil Field.

Hereunder the present invention will be detailed in embodiments. In thefollowing embodiments:

The palmitic acid is from Shanghai Aladdin Biochemical Technology Co.,Ltd., with designation as P101059;

The stearic acid is from Shanghai Aladdin Biochemical Technology Co.,Ltd., with designation as P108288;

The oleic acid is from Shanghai Aladdin Biochemical Technology Co.,Ltd., with designation as O108484;

The N-(2-ethoxyl) ethylene diamine is from Shanghai Aladdin BiochemicalTechnology Co., Ltd., with designation as H100513;

The infrared spectrometer is from Thermo Nicolet Corporation (a UScompany), with designation as Nexus;

The NMR spectrometer is from Bruker, with designation as AVANCE III HD400 Mhz.

Preparation Example 1

Palmitic acid and N-(2-ethoxyl) ethylene diamine (at a molar ratio of0.83:1) are dissolved in dimethyl benzene (the weight ratio of dimethylbenzene and N-(2-ethoxyl) ethylene diamine is 10:1), the obtainedmixture is loaded into a 250 mL three-neck flask equipped with a waterseparator, and treated by oil-bath heating and refluxing under amagnetic stirring condition, till all of the raw materials are dissolvedcompletely. The target heating temperature is set to 155° C., and themixture is held at the temperature for 5 h for reflux reaction, till thelevel of the interface between water and dimethyl benzene in the waterseparator has no change anymore (i.e., no more water separation); afterthe reaction is completed, unreacted N-(2-ethoxyl) ethylene diamine anddimethyl benzene solvent are separated and removed by rotaryevaporation, and thereby a crude product is obtained; the crude productis heated up to 230° C. in the three-neck flask while it is stirred, andis held at the temperature for 4 h for further reaction under a refluxcondensation condition, and finally a yellow oily liquid is obtained;the product is treated by reduced pressure distillation in hot state,the product is poured into a mixed solution of ethyl acetate, absoluteethyl alcohol, and petroleum ether mixed in advanced at a volume ratioof 3:3:1 before the product solidifies, the system is agitatedvigorously for 5 min. and then kept still so that a solid precipitatesare obtained; after the system is cooled and crystallized, it isfiltered by vacuum filtering, and flushed with the above-mentioned mixedsolution for 3 times; thus, a white semi-solid material is obtained; thewhite semi-solid material is dissolved in ether, and then the product istreated by vacuum filtering and washed for 3 times. The product iswrapped in a piece of filter paper, and is loaded into a vacuum dryingoven and dried for 24 hr; thus, the target product1-ethoxyl-2-pentadecyl-imidazoline is obtained.

The target product obtained in the preparation example 1 is measuredwith an infrared spectrometer and a NMR spectrometer respectively. Aninfrared spectrogram measured with the infrared spectrometer is shown inFIG. 1, wherein, the peak at 1,056.83 cm⁻¹ represents bending vibrationof —(CH₂)_(n)— in saturated long-chain alkyl; the peak at 2918.35 cm⁻¹represents symmetric bending vibration of C—H bond in —CH₃; the peak at3299.46 cm⁻¹ represents stretching vibration of —OH; the peak at 1640.22cm⁻¹ represents stretching vibration generated by C═N double bonds inimidazoline;

The H-NMR spectrogram measured with the NMR spectrometer is shown inFIG. 2: 1H NMR (400 MHz, Chloroform-d) δ 5.97 (s, 1H), 3.75-3.57 (m,2H), 3.37 (q, J=5.7 Hz, 2H), 2.97-2.51 (m, 4H), 2.23-2.11 (m, 2H),1.68-1.54 (m, 2H), 1.26 (d, J=12.5 Hz, 25H), 0.88 (t, J=6.8 Hz, 3H)

Preparation Example 2

Stearic acid and N-(2-ethoxyl) ethylene diamine (at a molar ratio of0.9:1) are dissolved in dimethyl benzene (the weight ratio of dimethylbenzene and N-(2-ethoxyl) ethylene diamine is 11:1), the obtainedmixture is loaded into a 250 mL three-neck flask equipped with a waterseparator, and treated by oil-bath heating and refluxing under amagnetic stirring condition, till all of the raw materials are dissolvedcompletely. The target heating temperature is set to 155° C., and themixture is held at the temperature for 5 h for reflux reaction, till thelevel of the interface between water and dimethyl benzene in the waterseparator has no change anymore (i.e., no more water separation); afterthe reaction is completed, unreacted N-(2-ethoxyl) ethylene diamine anddimethyl benzene solvent are separated and removed by rotaryevaporation, and thereby a crude product is obtained; the crude productis heated up to 230° C. in the three-neck flask while it is stirred, andis held at the temperature for 4 hr for further reaction under a refluxcondensation condition, and finally a yellow oily liquid is obtained;the product is treated by reduced pressure distillation in hot state,the product is poured into a mixed solution of ethyl acetate, absoluteethyl alcohol, and petroleum ether mixed in advanced at a volume ratioof 3:3:1 before the product solidifies, the system is agitatedvigorously for 5 min. and then kept still so that a solid precipitatesare obtained; after the system is cooled and crystallized, it isfiltered by vacuum filtering, and flushed with the above-mentioned mixedsolution for 3 times; thus, a white semi-solid material is obtained; thewhite semi-solid material is dissolved in ether, and then the product istreated by vacuum filtering and washed for 3 times. The product iswrapped in a piece of filter paper, and is loaded into a vacuum dryingoven and dried for 24 hr; thus, the target product1-ethoxyl-2-heptadecyl-imidazoline is obtained.

Preparation Example 3

Oleic acid and N-(2-ethoxyl) ethylene diamine (at a molar ratio of 1:1)are dissolved in dimethyl benzene (the weight ratio of dimethyl benzeneand N-(2-ethoxyl) ethylene diamine is 12:1), the obtained mixture isloaded into a 250 mL three-neck flask equipped with a water separator,and treated by oil-bath heating and refluxing under a magnetic stirringcondition, till all of the raw materials are dissolved completely. Thetarget heating temperature is set to 155° C., and the mixture is held atthe temperature for 5 hr for reflux reaction, till the level of theinterface between water and dimethyl benzene in the water separator hasno change anymore (i.e., no more water separation); after the reactionis completed, unreacted N-(2-ethoxyl) ethylene diamine and dimethylbenzene solvent are separated and removed by rotary evaporation, andthereby a crude product is obtained; the crude product is heated up to230° C. in the three-neck flask while it is stirred, and is held at thetemperature for 4 hr for further reaction under a reflux condensationcondition, and finally a yellow oily liquid is obtained; the product istreated by reduced pressure distillation in hot state, the product ispoured into a mixed solution of ethyl acetate, absolute ethyl alcohol,and petroleum ether mixed in advanced at a volume ratio of 3:3:1 beforethe product solidifies, the system is agitated vigorously for 5 min. andthen kept still so that a solid precipitates are obtained; after thesystem is cooled and crystallized, it is filtered by vacuum filtering,and flushed with the above-mentioned mixed solution for 3 times; thus, awhite semi-solid material is obtained; the white semi-solid material isdissolved in ether, and then the product is treated by vacuum filteringand washed for 3 times. The product is wrapped in a piece of filterpaper, and is loaded into a vacuum drying oven and dried for 24 hr;thus, the target product 1-ethoxyl-2-heptadecenyl-imidazoline isobtained.

Example 1

2.0 wt % 1-ethoxyl-2-pentadecyl-imidazoline obtained in the preparationexample 1, 0.4 wt % sodium p-toluenesulfonate, and 97.6 wt % water aremixed, to obtain a mobility control system A1.

Example 2

4.0 wt % 1-ethoxyl-2-pentadecyl-imidazoline obtained in the preparationexample 1, 0.6 wt % sodium p-toluenesulfonate, and 95.4 wt % water aremixed, to obtain a mobility control system A2.

Example 3

6.0 wt % 1-ethoxyl-2-pentadecyl-imidazoline obtained in the preparationexample 1, 0.8 wt % sodium p-toluenesulfonate, and 93.2 wt % water aremixed, to obtain a mobility control system A3.

Example 4

4.0 wt % 2-ethoxyl-2-heptadecyl-imidazoline obtained in the preparationexample 2, 0.6 wt % sodium salicylate, and 95.4 wt % water are mixed, toobtain a mobility control system A4.

Example 5

4.0 wt % 1-ethoxyl-2-heptadecenyl-imidazoline obtained in thepreparation example 3, 0.6 wt % maleic acid, and 95.4 wt % water aremixed, to obtain a mobility control system A5.

Example 6

2.0 wt % 1-ethoxyl-2-pentadecyl-imidazoline obtained in the preparationexample 1, 2.0 wt % 1-ethoxyl-2-heptadecyl-imidazoline obtained in thepreparation example 2, 2.0 wt % 1-ethoxyl-2-heptadecenyl-imidazolineobtained in the preparation example 3, 0.8 wt % sodiump-toluenesulfonate, and 93.2 wt % water are mixed, to obtain a mobilitycontrol system A6.

Example 7

4.0 wt % 1-ethoxyl-2-pentadecy-imidazoline obtained in the preparationexample 1, 0.2 wt % sodium p-toluenesulfonate, 0.2 wt % sodiumsalicylate, 0.2 wt % maleic acid, and 95.4 wt % water are mixed, toobtain a mobility control system A7.

Example 8

10.0 wt % 1-ethoxyl-2-pentadecyl-imidazoline obtained in the preparationexample 1, 0.1 wt % sodium p-toluenesulfonate, and 89.9 wt % water aremixed, to obtain a mobility control system A8.

Example 9

1.0 wt % 1-ethoxyl-2-pentadecyl-imidazoline obtained in the preparationexample 1, 2.0 wt % sodium p-toluenesulfonate, and 97.0 wt % water aremixed, to obtain a mobility control system A9.

Example 10

4.0 wt % 1-ethoxyl-2-pentadecyl-imidazoline obtained in the preparationexample 1, 0.6 wt % sodium salicylate, and 95.4 wt % water are mixed, toobtain a mobility control system A10.

Measurements

-   -   (1) Viscosity of the mobility control system: The viscosity        values of A1-A10 sheared at 25° C. and 7.34 s⁻¹ shearing rate        for 10 min are measured respectively with a rheometer (from        Thermo Fisher SCIENTIFIC, with designation as Haake MARS 60, the        same below). The result is shown in Table 1.    -   (2) Viscosity of the plugging agent for gas channeling formed by        the mobility control system: Carbon dioxide is introduced (at        1.0 ml/min introducing rate, the volume ratio of the introduced        volume of carbon dioxide and the volume of the mobility control        system is 1:1) into the mobility control systems A1-A10 at        different temperatures (40° C., 65° C., and 90° C.)        respectively, to form plugging agents for gas channeling. The        viscosity values of the plugging agents for gas channeling        sheared at corresponding temperatures and 7.34 s⁻¹ shearing rate        for 10 min are measured respectively with a rheometer. The        result is shown in Table 2.    -   (3) Plugging efficiency under different fracture and temperature        conditions: the plugging efficiency of each of the mobility        control systems A1-A10 in factures in different widths (50 μm,        300 μm, and 900 μm) at different temperatures (40° C., 65° C.,        and 90° C.) is tested respectively with the plugging efficiency        testing method described in the present invention. The result is        shown in Table 3.

TABLE 1 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 Viscosity, mPa · s 5 5 6 7 8 10 76 5 7

It can be seen from the result in Table 1: the mobility control systemin the present invention has initial viscosity as low as 5-10 mPa·s, andhas favorable injection performance. It can penetrate into the deepchannel easily, so that the deep channels are plugged off.

TABLE 2 Viscosity of Plugging Agent for Gas Channeling Formed atDifferent Temperatures, mPa · s 40° C. 65° C. 90° C. A1 5.0 × 10⁴ 4.2 ×10⁴ 2.6 × 10⁴ A2 7.0 × 10⁴ 6.0 × 10⁴ 4.5 × 10⁴ A3 12.0 × 10⁴  10.0 ×10⁴  7.0 × 10⁴ A4 5.8 × 10⁴ 4.4 × 10⁴ 3.0 × 10⁴ A5 6.2 × 10⁴ 5.1 × 10⁴3.1 × 10⁴ A6 10.1 × 10⁴  8.6 × 10⁴ 6.0 × 10⁴ A7 6.3 × 10⁴ 5.3 × 10⁴ 3.2× 10⁴ A8 4.5 × 10⁴ 3.8 × 10⁴ 2.2 × 10⁴ A9 2.6 × 10⁴ 2.0 × 10⁴ 1.2 × 10⁴A10 5.2 × 10⁴ 4.3 × 10⁴ 2.7 × 10⁴

It can be seen from the result in Table 2: the mobility control systemin the present invention interacts with carbon dioxide and form aplugging agent for gas channeling that has viscosity as high as1×10⁴-20×10⁴ mPa·s at 40-90° C., which is favorable for deep plugging incarbon dioxide flooding oil reservoirs, and can increase the sweptvolume of carbon dioxide flooding. Moreover, it can be seen intuitivelyfrom FIG. 3: the viscosity of the plugging agent for gas channelingformed by the mobility control system in the present invention andcarbon dioxide is remarkably increased, which indicates that themobility control system in the present invention has highly carbondioxide sensitivity.

TABLE 3 Plugging Efficiency under Different Fracture and TemperatureConditions, % Temperature 40° C. 65° C. 90° C. Width of fracture 50 μm300 μm 900 μm 50 μm 300 μm 900 μm 50 μm 300 μm 900 μm A1 96.3 93.5 90.694.8 91.5 87.6 93.3 88.5 81.6 A2 98.6 94.8 91.3 97.1 92.8 88.3 95.6 89.882.3 A3 99.4 96.4 91.9 97.9 94.4 88.9 96.4 91.4 82.9 A4 96.9 94.0 90.795.4 92.0 87.7 93.9 89.0 81.7 A5 97.0 94.2 90.9 95.5 92.2 87.9 94.0 89.281.9 A6 99.0 95.8 91.6 97.5 93.8 88.6 96.0 90.8 82.6 A7 97.4 94.6 91.195.9 92.6 88.1 94.4 89.6 82.1 A8 96.1 92.6 90.3 94.6 90.6 87.3 93.1 87.681.3 A9 94.1 92.3 90.0 92.6 90.3 87.0 91.1 87.3 81.0 A10 96.6 93.8 90.595.1 91.8 87.5 93.6 88.8 81.5

It can be seen from the result in Table 3: the mobility control systemin the present invention interacts with carbon dioxide in cores andthereby forms a plugging agent for gas channeling that has outstandingplugging performance.

While the present invention is described above in detail in somepreferred embodiments, the present invention is not limited to thoseembodiments. Various simple variations, including combinations of thetechnical features in any other appropriate way, can be made to thetechnical scheme of the present invention within the scope of thetechnical concept of the present invention, but such variations andcombinations shall be deemed as disclosed content in the presentinvention and falling in the protection scope of the present invention.

We claim:
 1. A mobility control system comprising the imidazolinecompound represented by formula (1), a mobility control additive, andwater;

wherein R is pentadecyl, and the mobility control additive is sodiump-toluene sulfonate.
 2. The mobility control system of claim 1, wherein,as percentages of the weight of the mobility control system, the contentof the imidazoline compound is 1-10 wt. %, the content of the mobilitycontrol additive is 0.1-2 wt. %, and the content of water is 88-98.9 wt.%.
 3. The mobility control system of claim 2, wherein, as percentages ofthe weight of the mobility control system, the content of theimidazoline compound is 2-6 wt. %, the content of the mobility controladditive is 0.4-0.8 wt. %, and the content of water is 93.2-97.6 wt. %.4. A plugging agent for gas channeling, wherein the plugging agent forgas channeling is a mixture obtained by introducing carbon dioxide intothe mobility control system of claim 1 to form a gel.
 5. The pluggingagent for gas channeling of claim 4, wherein, as percentages of theweight of the mobility control system, the content of the imidazolinecompound is 1-10 wt. %, the content of the mobility control additive is0.1-2 wt. %, and the content of water is 88-98.9 wt. %.
 6. The pluggingagent for gas channeling of claim 4, wherein, as percentages of theweight of the mobility control system, the content of the imidazolinecompound is 2-6 wt. %, the content of the mobility control additive is0.4-0.8 wt. %, and the content of water is 93.2-97.6 wt. %.